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KMID : 0381019920250060492
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Korean Journal of Nutrition
1992 Volume.25 No. 6 p.492 ~ p.500
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The Effect of Excess Dietary Vitamin A on vitamin K-dependent Carboxylation in Rat Liver Microsomes
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Lee Il-Ha
Dorothy M. Morre
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Abstract
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The rate of vitamin K-dcpendent carboxylation of endogenous liver microsomal proteins and an exogenous peptide substrate for carboxylase were measured to test the effects of excess vitamin A on vitamin K function in rats. In vitro vitamin A incubation in normal rat microsomes of vitamin K-sufficient rats did not mfluence the carboxylation rates of either endogenous prothrombin precursors or a peptide substrate added. Similarly, vitamin A incubation in tnicrosomes
from control and excess vitamin A-fed rats that were on vitamin K-free diet did not change the rate significantly within the respective groups ; however, the rates of endogenous protein carboxylation from excess vitamin A-fed rats tended to be increased by the in vitro vitamin A addition compared to that of control rats. Excess vitamin A-fed rats had 2- to 3fold
higher carboxylase activities of endogenous protein carboxylation either with or without the in vitro vitamin A incubation than did control rats. In an in vivo study, carboxylase activities with an added exogenous peptide substrate were not influenced by excess intake of vitamin A. However, the endogenous protein carboxylation rate was about 2- to 3- fold higher for excess vitamin A-fed rats than for control rats. Carboxylase activities tended to be increased in both control and excess vitamin A-fed rats as the study progressed . The effect of excess amounts of vitamin A on endogenous protein carboxylation appeared as early as one week post-initiation of the diet The result of this study indicate that excess vitamin A produces toxic effect rapidly, and that excess dietary vitamin A increase the rate of carboxylation of endogenous protein, mainly prothrombin precursors, which is an indication of vitamin K deficiency.
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KEYWORD
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Vitamin A, Vitamin K, Vitamin K-dependent carboxylase activity
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